Conventionally, a navigation apparatus guides a route to a predetermined destination and displays a map of any area. In the navigation apparatus, map data is read out from a memory medium such as a CD-ROM, a DVD-ROM and a HDD, and route setting and map display are performed. Here, an actual road may be changed or newly built. Thus, the map data preliminary stored in the memory medium does not include new map data for a portion in which the road is changed or newly built.
In view of the above point, for example, the new map data in each area is obtained from a control center for controlling the map data via a communication network and updated. Another method is disclosed in JP-A-2003-296884, JP-A-2004-85405 and JP-A-2007-93260 such that the new map data in each area is obtained from another navigation apparatus in another vehicle via an inter-vehicle communication system and updated.
When all of the map data in all of area is obtained and updated, a communication cost increases, or load of the control center increases. Thus, it is practical to obtain and update a part of the map data for a part of an area. An apparatus for updating only a part of the map data is disclosed in, for example, JP-A-2007-64951. In this apparatus, latest map data corresponding to old map data is obtained via the inter-vehicle communication system, and the latest map data is stored in the apparatus. Further, in JP-A-2007-65042, a deficient part of the map data for showing a map around a current position of the vehicle is firstly obtained via the inter-vehicle communication system, and the map data is updated. In JP-A-2005-147864, the latest map data corresponding an area including the same type of a POI (point of interest) as a POI of an area through which the vehicle has passed in the past, a POI of the destination and a POI of a point on the route to the destination is obtained via the inter-vehicle communication system, and the map data is updated.
However, in the techniques described in JP-A-2007-64951, JP-A-2007-65042 and JP-A-2005-147864, a part of the map data corresponding to a part of an area is updated, so that a communication cost is reduced, and a load of the center is reduced. However, the map data corresponding to a comparatively large area is not effectively updated.
Specifically, in the navigation apparatus disclosed in JP-A-2007-64951, only a part of the map data corresponding to an area including a route, which has been searched, is updated. Thus, other part of the map data corresponding to an area not including a route, which has been searched, is not updated.
In a map data updating system disclosed in JP-A-2007-65042, a part of the map data corresponding to an area around the vehicle among the deficient part of the map data is updated preferentially. Thus, other part of the map data corresponding to an area other than the area around the vehicle is not updated easily.
In a method for updating map data disclosed in JP-A-2005-147864, only the latest map data corresponding an area including the same type of the POI as the POI of an area through which the vehicle has passed in the past, a POI of the destination and a POI of a point on the route to the destination is updated. Thus, only the map data corresponding to a certain area is updated.